1. Field of the Invention
This invention relates to gravitational and air classification of a mixture of particles in a trash reclamation system.
2. Description of the Prior Art
The field of air classification or separation is not new, but has remained somewhat static until the logistics and economics of the contemporary society prompted renewed interest in research to invent better and less costly ways of disposing of the vast quantities of trash produced each day, while, at the same time, allowing the recovery of valuable constituents contained in the trash. Two of the prior art techniques can be seen by reference to FIG. 1. In the first, a mixture 10 of heavy 12, light 14 and fine 16 particles (such as shredded trash) is deposited into an input hopper 18 which ends in an air blocking device 20. The air blocking device 20 delivers the mixture 10 to input conduit 22 while, at the same time, prohibiting the flow of air 24 out through input hopper 18. Air 24 is induced (as by vacuum) into vertical conduit 26 from the bottom to the top as shown in FIG. 1. As the mixture 10 is deposited into vertical conduit 26, gravity 28 tends to pull the particles 12, 14 and 16 down while the air 24 tries to blow them up. The light 14 and fine 16 particles are blown upward by air 24 while the heavy particles 12 fall out the bottom.
Air classification in the second form takes place in the cyclone 30 of FIG. 1. Air 24, light 14 and fine 16 particles enter cyclone 30 tangentially. While air 24 rising in the narrower vertical conduit 26 could support the weight of particles 14 and 16, in cyclone 30 air 24 moves tangentially about the inner periphery of cyclone 30, changes direction, and exits through exit duct 32. Because of the centrifugal force and the larger area in cyclone 30, the light particles 14 can no longer be supported by air 24 and drop out the bottom. Fine particles 16 continue with air 24.
Another prior art air classification system combining elements of the vertical column and cyclone is shown in FIG. 2. Heavy particles 40 and light particles 42 drop into air classifier 44 at inlet 46 along with parallel air 48 and proceed to the bottom of classifier 44 where the main air flow path doubles back toward light outlet 50. Centrifugal force and gravity act on particles 40 and 42 to resist their rising toward light outlet 50. Additionally, fluidizing air 52 and counter flow air 54 are injected to assist the rising air force of parallel air 48. As a result, light particles 42 rise and exit through light outlet 50, while the heavy particles 40 pass out through outlet 56.
A simple form of pure horizontal flow air classifier is shown in FIG. 3. Material 60 enters the classifier 62 at inlet 64 along with parallel air 66. Since the horizontal force of air 66 is constant, the horizontal acceleration of the particles of material 60 is inversely proportioned to mass (Force = mass .times. acceleration). When the material 60 enters the classifier 62 it is accelerated down by gravity while continuing forward as a function of its horizontal acceleration and velocity. Heavy particles 68 fall into the bin closest to inlet 64 while lighter particles move further along. Fines 70 are carried by air 66 and must be removed by a filter 72.
All these prior art devices work in their fashion to a degree, depending on the application. Cyclones such as that of FIG. 1, for example, have been used successfully for years in the lumber business to carry off undesired sawdust and wood chips. A light dry homogeneous material lends itself ideally to air classification. Unfortunately, domestic and industrial waste does not fall into that category. Trash is a variable both in material content and moisture content and to be successful, a classifier must be able to handle any and all material to accepted standards. One major problem is moisture. Wet lights stuck together tend to respond as a heavy. Thus, in apparatus such as that of FIG. 2 vibrating means are often attached to the device to attempt breakup of clumps entering the classifier and removal of material tending to stick at the bottom of the drop area. Another helpful technique is the pulverizing of the material into smaller particles prior to classification. Pulverizing, however, takes energy. The smaller the end particles, the more energy required. Likewise, raising particles vertically against gravity takes more energy than moving the same particles horizontally. The more the cost of recovery of useful material from trash, the less the incentive to do so. Along the same line, the more complex the apparatus, the higher the initial investment and more likely the need for repair with attendant cost and down time.
In their U.S. Pat. No. 3,799,339 (copy enclosed herewith) Breitholtz and Lindberg disclose a simple apparatus using horizontal air flow to remove rocks from light particulate matter. Unfortunately, its use in trash classifiation, as is the prime objective of the present invention, is limited to a final purification of the previously classified light material as shown in the sales material of the patent's assignee (copy enclosed herewith) and as will become apparent in the description of the present invention to follow hereinafter.
Thus, it is the prime objective of the present invention to provide a horizontal flow air classifier for use with heterogeneous waste materials.
It is a further object of the present invention to provide an air classifier for heterogeneous waste which is simple in design with virtually no critical wearing parts.
It is yet another object of the present invention to provide an air classifier for heterogeneous waste requiring minimal energy in the preparation of said waste prior to classification and minimal energy in the classification of said waste.